Fall in Traffic After Changing Preffered Domain in Webmaster

Hey SEO Experts,
Today , I have read preferred domain settings and change preferred domain to www.mydomain.com .... after changing there is a huge fall in the traffic. Can anybody guide me in this permanent or temporary ?? I am too much worried

 

I also made some changes in the .htaccess file and now the recent one if

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]

RewriteCond %{HTTP_HOST} .
RewriteCond %{HTTP_HOST} !^www\.stayupdated\.info$
RewriteRule (.*) http://www.stayupdated.info/$1 [R=301,L]

</IfModule>


<IfModule mod_headers.c>
Header set Content-Security-Policy "script-src 'self'; object-src 'self'"
<FilesMatch "\.(appcache|atom|crx|css|cur|eot|f4[abpv]|flv|gif|htc|ico|jpe?g|js|json(ld)?|m4[av]|manifest|map|mp4|oex|og[agv]|opus|otf|pdf|png|rdf|rss|safariextz|svgz?|swf|tt[cf]|vcf|vtt|webapp|web[mp]|woff|xml|xpi)$">
Header unset Content-Security-Policy
</FilesMatch>
</IfModule>
<IfModule mod_autoindex.c>
    Options -Indexes
</IfModule>


<FilesMatch "(^#.*#|\.(bak|config|dist|fla|in[ci]|log|psd|sh|sql|sw[op])|~)$">

    # Apache < 2.3
    <IfModule !mod_authz_core.c>
        Order allow,deny
        Deny from all
        Satisfy All
    </IfModule>

    # Apache ≥ 2.3
    <IfModule mod_authz_core.c>
        Require all denied
    </IfModule>

</FilesMatch>




<IfModule mod_rewrite.c>
    RewriteCond %{SCRIPT_FILENAME} -d [OR]
    RewriteCond %{SCRIPT_FILENAME} -f
    RewriteRule "(^|/)\." - [F]
</IfModule>

<IfModule mod_expires.c>

    ExpiresActive on
    ExpiresDefault "access plus 1 month"

  # CSS
    ExpiresByType text/css "access plus 1 year"

  # Data interchange
    ExpiresByType application/json "access plus 0 seconds"
    ExpiresByType application/ld+json "access plus 0 seconds"
    ExpiresByType application/xml "access plus 0 seconds"
    ExpiresByType text/xml "access plus 0 seconds"

  # Favicon (cannot be renamed!) and cursor images
    ExpiresByType image/x-icon "access plus 1 week"

  # HTML components (HTCs)
    ExpiresByType text/x-component "access plus 1 month"

  # HTML
    ExpiresByType text/html "access plus 0 seconds"

  # JavaScript
    ExpiresByType application/javascript "access plus 1 year"

  # Manifest files
    ExpiresByType application/x-web-app-manifest+json "access plus 0 seconds"
    ExpiresByType text/cache-manifest "access plus 0 seconds"

  # Media
    ExpiresByType audio/ogg "access plus 1 month"
    ExpiresByType image/gif "access plus 1 month"
    ExpiresByType image/jpeg "access plus 1 month"
    ExpiresByType image/png "access plus 1 month"
    ExpiresByType video/mp4 "access plus 1 month"
    ExpiresByType video/ogg "access plus 1 month"
    ExpiresByType video/webm "access plus 1 month"

  # Web feeds
    ExpiresByType application/atom+xml "access plus 1 hour"
    ExpiresByType application/rss+xml "access plus 1 hour"

  # Web fonts
    ExpiresByType application/font-woff "access plus 1 month"
    ExpiresByType application/vnd.ms-fontobject "access plus 1 month"
    ExpiresByType application/x-font-ttf "access plus 1 month"
    ExpiresByType font/opentype "access plus 1 month"
    ExpiresByType image/svg+xml "access plus 1 month"

</IfModule>

# -----------------------------------------------------------------------
# Compressing output.
# -----------------------------------------------------------------------
<IfModule mod_deflate.c>
    AddOutputFilterByType DEFLATE text/html text/plain text/css application/json
    AddOutputFilterByType DEFLATE application/javascript
    AddOutputFilterByType DEFLATE text/xml application/xml text/x-component
    AddOutputFilterByType DEFLATE application/xhtml+xml application/rss+xml application/atom+xml
    AddOutputFilterByType DEFLATE image/x-icon image/svg+xml application/vnd.ms-fontobject application/x-font-ttf font/opentype
</Ifmodule>

# END WordPress

Code (markup):

 

Finally issue is resolved. Problem was not due to preferred domain setting but due to htaccess. I am unable to locate exact location in the htaccess file but I removed all the other data and now my latest htaccess working well with www URL and IP canonicalization is

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
RewriteCond %{HTTP_HOST} .
RewriteCond %{HTTP_HOST} !^www\.stayupdated\.info$
RewriteRule (.*) http://www.stayupdated.info/$1 [R=301,L]
</IfModule>
#End WordPress

Code (markup):